Spermatogonia are the male germ line stem cells whose life long expansion is needed for permanent production of spermatozoa. The present study was designed to examine the effect of hCG treatment on germ cell proliferation following stem cell transplantation in mice. Spermatogonial stem cells were isolated from neonatal mice testes and characterized by alkaline phosphatase, immunoreactivity and morphological analysis. hCG was injected into normal and cell transplanted mice. We then evaluated the testosterone levels and cell number in normal mice. After that, cyclin B1 gene expression was investigated in transplanted mice. Different doses of busulfan were injected to investigate the effects of chemotherapy on morphological criteria and preparation of recipient mice for transplantation. In this report we show proliferative potential of spermatogonial stem cells after cytotoxic treatment, transplantation efficiency by semi-quantitative RT-PCR, and hCG effect on stem cell regeneration in normal mice and following cell transplantation. The results indicate that spermatogonial stem cells can proliferate after transplantation, and the efficiency of their transplantation depends on hormonal treatment. Therefore, hormonal treatment after stem cell transplantation will be a powerful avenue for increasing the efficiency of transplantation and fertility restoration.